Image Formats Explained: JPG, PNG, WebP, HEIC, GIF & BMP
Your files end in .jpg, .png, .webp, .heic — and it is never obvious which one to use or why a form rejects some of them. Image formats are one of those quietly confusing topics that cause real headaches at upload time. This guide clears it up: what each common format is, what it is good and bad at, and which to choose for any situation.
By the end you will know exactly why forms want JPG, when PNG is worth its larger size, and what to do with an iPhone's HEIC files.
Why there are so many formats
Different formats exist because images have different jobs. A photograph, a logo, a screenshot, and an animation all have different needs — some want tiny file sizes, some want perfect detail, some want transparency, some want motion. No single format does everything well, so several evolved, each optimised for a purpose. Knowing which job you have makes choosing the format easy.
The two big families: lossy and lossless
Before the individual formats, one idea explains most of the differences. Lossy formats shrink files by permanently discarding detail your eye is unlikely to miss — great for small files, not perfect quality. Lossless formats keep every pixel exactly, so quality is perfect but files are larger. JPG and (usually) WebP are lossy; PNG, GIF and BMP are lossless. This single distinction drives which format suits which job.
JPG / JPEG — the everyday photo format
JPG (also written JPEG) is the workhorse of digital photography. It is lossy, compressing photographs to small files while looking great at normal sizes. It is supported absolutely everywhere — every device, browser, app and government portal reads it. That universal support, plus its small file sizes, is why forms almost always ask for JPG.
Best for: photographs, passport photos, signatures, anything going to a form. Weak at: sharp-edged graphics and text, where it can add fuzzy halos, and transparency, which it cannot store. Rule of thumb: if it is a photo or an upload, use JPG.
PNG — perfect quality and transparency
PNG is lossless, so it keeps every pixel exactly, and it supports transparency, which lets part of the image be see-through. This makes it ideal for logos, icons, screenshots and graphics with hard edges. The trade-off is size: a photograph saved as PNG is several times larger than the same photo as JPG, which is why photo-PNGs so often fail a form's KB limit.
Best for: logos, icons, screenshots, line art, anything needing transparency or crisp edges. Weak at: photographs, where it wastes space. Rule of thumb: use PNG for graphics, not photos.
WebP — the modern all-rounder
WebP is a newer format that can work in both lossy and lossless modes, and in both it usually produces smaller files than the older formats — a lossy WebP beats JPG at the same quality, and a lossless WebP beats PNG. It also supports transparency and animation. On paper it is the best of every world.
The catch is acceptance. Browsers handle WebP well, so it is excellent for websites and makes pages load faster. But many government and exam portals do not accept it for uploads yet. So WebP is a great choice for your own website but a poor choice for a form — convert it to JPG before uploading.
HEIC — the iPhone format
HEIC is Apple's space-saving photo format, storing a photo at the same quality as a JPG in about half the space. That is handy on your phone, but HEIC is poorly supported outside Apple devices, so most forms and many websites reject it. This catches out huge numbers of people, whose perfectly good iPhone photo is refused simply for being HEIC.
Best for: storing photos on an iPhone. Weak at: compatibility — most forms will not take it. Rule of thumb: convert HEIC to JPG before uploading anywhere, or set your iPhone camera to "Most Compatible" so it shoots JPG.
GIF — animation and simple graphics
GIF is an old format best known for short, looping animations. It is lossless but limited to 256 colours, which makes it poor for photographs — they look banded and blocky — but fine for simple graphics and animations. You will rarely use GIF for a form; if you have a still frame you need as a photo, convert it to JPG.
Best for: simple animations and low-colour graphics. Weak at: photographs and anything needing many colours. Rule of thumb: not for form photos.
BMP — old and uncompressed
BMP is an old, essentially uncompressed format, which makes its files enormous — many times larger than a JPG of the same image. It is rarely used today, and you should convert any BMP to JPG before uploading, both to meet size limits and because many forms do not accept it. If you find a surprisingly huge image file, checking whether it is a BMP is worth doing.
Best for: almost nothing in modern use. Weak at: file size. Rule of thumb: convert to JPG.
TIFF — high quality for print and archives
You may occasionally meet TIFF, a high-quality format used in printing, scanning and archiving. It preserves maximum detail and is often very large. It is not meant for the web or form uploads, so if a scanner hands you a TIFF and you need to upload it, convert to JPG (or PDF for a document) at a sensible size first.
A quick comparison
- JPG — lossy, small, universal. Best for photos and uploads.
- PNG — lossless, larger, transparent. Best for graphics and screenshots.
- WebP — smaller than both, modern, but poorly accepted by forms.
- HEIC — small, iPhone-only, rejected by most forms.
- GIF — animation and simple graphics, not photos.
- BMP — old and huge, convert it.
- TIFF — print and archive quality, very large, convert for uploads.
Which format should you use for a form?
Almost always JPG. Forms want small, universally readable files, and JPG delivers both. The only exceptions are the rare forms that specifically ask for PNG, usually for a signature or a document with sharp text. If your image is currently a PNG, WebP, HEIC, BMP or TIFF, convert it to JPG before uploading, which also usually shrinks it enough to fit the size limit.
How to convert between formats
You do not need special software. Built-in editors like Paint on Windows and Preview on Mac can open one format and save as another. A browser tool is often easier, especially on a phone: open imageto10kb, choose your image, set the output to JPEG, pick a target size, and download. That converts and compresses in one step, in your browser, with nothing uploaded.
Does converting formats lose quality?
It depends on the direction. Converting a lossless PNG to a lossy JPG applies compression once, a small and usually invisible change for a photo, well worth it for the smaller size. Converting between two lossy formats, or re-saving the same JPG many times, stacks up quality loss, so convert once from your best original. Converting to a lossless format never adds quality back — it just wraps the existing image in a bigger file.
Common format mistakes
- Renaming instead of converting — changing
.pngto.jpgin the file name does not convert it and can break the file. Re-save it properly. - Uploading HEIC to a form — convert iPhone photos to JPG first.
- Saving a photo as PNG — it will be too big for most limits; use JPG.
- Trying to upload WebP to a portal that only takes JPG.
- Ignoring a huge BMP or TIFF — convert to JPG to shrink it dramatically.
How to tell what format a file is
On a computer the easiest way is the file extension at the end of the name — .jpg, .png, .webp, .heic and so on. If extensions are hidden, right-click the file and check its properties or get-info panel, which lists the type. On a phone it is less obvious, which is exactly why HEIC catches people out: a photo that looks perfectly normal in your gallery may quietly be a HEIC file. When you are unsure and about to upload, the safe move is to run the image through a tool set to JPEG output, so you know the result is a valid JPG regardless of what it started as.
Format and file size: a quick example
The size difference between formats is bigger than most people expect. A typical passport-style photo might be around 1,500KB as a PNG, roughly 700KB as a BMP-style uncompressed file, and only about 120KB as a JPG — all at the same dimensions and with no visible difference at that size. The same photo as a lossless format is many times heavier than as JPG. This is the whole reason forms standardise on JPG: it lets them accept a clear photo while keeping the file tiny, which no lossless format can match for a photograph.
What about RAW camera files?
If you use a proper camera, you may have RAW files, with extensions like .cr2, .nef or .arw. RAW captures everything the sensor recorded, which is wonderful for editing but produces enormous files that no form or website accepts. RAW is a working format, not a sharing one. Export or convert your edited RAW to JPG at a sensible size before uploading it anywhere. Treat RAW like a negative: you keep it to work from, but you hand out the JPG.
Formats and transparency
Transparency is one of the clearest reasons to choose one format over another. PNG and WebP can store transparent areas, so parts of the image are see-through — essential for a logo that sits on different backgrounds. JPG cannot store transparency at all; when you convert a transparent image to JPG, those areas fill with a solid colour, usually white. For a photo this never matters, since photos have no transparency, but for a logo or a cut-out graphic, keep it as PNG unless you deliberately want a solid background.
A note on animated images
If you need motion, only a few formats support it: GIF is the classic, and WebP can also animate, as can the newer APNG. Static formats like JPG and PNG cannot hold animation — saving an animation as JPG gives you a single frozen frame. Forms almost never want animated images, so if you have an animation and need a still, export or screenshot a single frame and save that as JPG. For the web, an animated WebP is far smaller than the equivalent GIF and looks better.
Troubleshooting checklist
- Is your upload a JPG? If not, convert it.
- Is it an iPhone HEIC? Convert to JPG.
- Is a photo saved as PNG and too big? Convert to JPG.
- Did you actually re-save, not just rename the extension?
- Does the file open and look correct after converting?
The bottom line
There is no single best image format — there is a best format for each job. For photographs and, above all, for anything you upload to a form, JPG wins because it is small and readable everywhere. For logos, screenshots and anything needing transparency or crisp edges, PNG is the right tool. WebP is excellent for your own website but poorly accepted by forms, and HEIC, BMP and TIFF should all be converted to JPG before you upload them. Match the format to the content, convert to JPG when in doubt about an upload, and always re-save rather than just renaming the extension — get those habits right and format problems simply stop happening.
Frequently asked questions
What is the best image format?
There is no single best — it depends on the job. JPG is best for photos and form uploads, PNG for graphics and transparency, WebP for websites. For anything you are uploading to a form, JPG is almost always the right answer.
Why does a form only accept JPG?
Because JPG produces small files and is readable on every device, which keeps the portal fast and simple. Convert other formats to JPG before uploading.
Is JPG or PNG better?
For photographs, JPG — it is far smaller with no visible loss at normal sizes. For logos, screenshots and transparency, PNG — it keeps perfect quality and hard edges. Match the format to the content.
How do I convert HEIC to JPG?
Open the HEIC in a tool that lets you choose JPEG output — a browser tool like imageto10kb does it and compresses to a target size, in your browser. On iPhone, you can also set the camera to "Most Compatible" in Settings so it shoots JPG from the start, which avoids the conversion entirely for future photos.
Is WebP good for uploads?
Not usually. WebP is great for websites because it is small, but most forms do not accept it yet. Convert WebP to JPG before uploading to a form. On your own website, though, WebP is an excellent choice because its smaller files help pages load faster, which is good for both visitors and search rankings.
Quick tip: for form uploads the answer is almost always JPG — it is small and universally accepted. Keep PNG for graphics and transparency, and convert HEIC, WebP, BMP and TIFF to JPG before you upload, which usually shrinks them enough to fit the size limit as well.